Disk device with low profile housing having an increased holding capacity of magnetic disks

ABSTRACT

According to one embodiment, a disk device includes a housing with a bottom wall, magnetic disks supported on a hub of a motor, a printed circuit board provided on an outer surface of the bottom wall, and a wiring board attached on the outer surface of the bottom wall. The bottom wall includes a recess formed in the outer surface, a step located on border between the outer surface and the recess, and through holes opened to the recess. The wiring board includes one end portion disposed in the recess and connection pads on the one end portion, connected to lead wires of a coil. An adhesive is filled into the recess and the through holes, and covers the one end and a solder joint and seals the through holes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation if U.S. application Ser. No.17/016,878 filed on Sep. 10, 2020 and is based upon and claims thebenefit of priority from Japanese Patent Applications No. 2020-031684,filed Feb. 27, 2020; and No. 2020-119893, filed Jul. 13, 2020, theentire contents of all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a disk device.

BACKGROUND

As a disk drive, for example, a hard disk drive (HDD) comprises aplurality of magnetic disks disposed rotatably in a housing, a pluralityof magnetic heads which carry out read or write of data from/to amagnetic disk, and a head actuator movably supporting the magnetic headswith respect to the respective magnetic disks. A spindle motor isinstalled on a bottom wall of the housing, and magnetic disks aremounted to a cylindrical hub of the spindle motor.

Recently, such a housing is air-tightly constructed, and a low-densitygas such of helium or the like is enclosed in the housing. Further, inorder to increase the storage capacity, there have been attempts to loadmore magnetic disks in the housing.

In order for such disk drives as described above to be able to sustainthe sealing of a low-density gas for a long term, a high cast-qualityhousing with only few casting cavities, which may give rise to leakpaths, is required. In order to improve the fluidity of the moltenmaterial while casting, the thickness of at least about 1 mm isnecessary for the cast product. Further, in order to avoid the hub ofthe motor rotating at high speed from being brought into contact withthe bottom wall of the housing, a predetermined gap needs to be providedbetween the flange of the hub and the bottom wall. However, therenecessary items can be an obstacle in the attempt to increase the numberof disks to be mounted or to expand the intervals between disks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a hard disk drive (HDD)according to the first embodiment when the top cover is removed.

FIG. 2 is a plan view of a rear surface of the HDD.

FIG. 3 is a partially enlarged plan view showing a motor connectionportion shown in FIG. 2 .

FIG. 4 is a cross section of the HDD taken along line A-A in FIG. 2 .

FIG. 5 is a cross section of an HDD according to the second embodiment.

DETAILED DESCRIPTION

Various embodiments will be described hereinafter with reference to theaccompanying drawings. In general, according to one embodiment, a diskdevice comprises a housing comprising a base including a bottom wall anda cover fixed to the base; a motor comprising a shaft provided on thebottom wall, a hub including an outer circumferential surface coaxialwith the shaft and an annular flange provided on the outercircumferential surface, and rotatably supported on the shaft, and acoil provided around the shaft; a plurality of magnetic disks attachedto the hub to overlap the flange; a head actuator supporting a pluralityof magnetic heads and installed rotatably in the housing; a printedcircuit board disposed to oppose an outer surface of the bottom wall;and a wiring board attached on the outer surface of the bottom wall andelectrically connected to the printed circuit board and the coil. Thebottom wall includes a recess formed in the outer surface to oppose aregion between an inner circumferential edge of the flange and theshaft, a step located on a border between the outer surface and therecess, and through holes each formed to penetrate the bottom wall andopened to the recess. The wiring board includes one end portion disposedin the recess and a plurality of connection pads provided on the one endportion, the coil includes lead wires drawn out in the recess via thethrough holes, and joined to the connection pads by soldering, and anadhesive is filled into the recess and the through holes, covering theone end and a solder joint, and sealing the through holes.

The disclosure is merely an example, and proper changes in keeping withthe spirit of the invention, which are easily conceivable by a person ofordinary skill in the art, come within the scope of the invention as amatter of course. In addition, in some cases, in order to make thedescription clearer, the widths, thicknesses, shapes and the like, ofthe respective parts are illustrated schematically in the drawings,rather than as an accurate representation of what is implemented.However, such schematic illustration is merely exemplary, and in no wayrestricts the interpretation of the invention. In addition, in thespecification and drawings, the same elements as those described inconnection with preceding drawings are denoted by like referencenumbers, and detailed description thereof is omitted unless necessary.

First Embodiment

As a disk device, a hard disk drive (HDD) of a first embodiment will bedescribed in detail.

FIG. 1 is an exploded perspective view of a hard disk drive (HDD)according to the first embodiment when the top cover is removed.

As shown, the HDD comprises substantially a rectangular-shaped housing10. The housing 10 includes a rectangular box-shaped base 12 whose uppersurface is opened, an inner cover 14 screwed to the base 12 with aplurality of screws 13 and closing an upper edge opening of the base 12and an outer cover (a top cover) 16 disposed to be overlaid on the innercover 14, whose circumferential portion is welded to the base 12. Thebase 12 includes a rectangular-shape bottom wall 12 a opposing the innercover 14 with a gap therebetween and a side wall 12 b provided to standalong the circumference of the bottom wall 12 a, formed to be integratedas one body, for example, aluminum alloy. The side wall 12 b includes apair of long side walls opposing each other and a pair of short sidewalls opposing each other. On an upper end surface of the side wall 12b, a substantially rectangular frame-shaped fixation rib 12 c isprovided to project therefrom.

The inner cover 14 is formed, for example, of stainless steel into arectangular plate shape. The inner cover 14 is fixed inside the fixationrib 12 c by screwing the circumferential portion of the cover to theupper end surface of the side wall 12 b with screws 13. The outer cover16 is formed, for example, of aluminum into a rectangular plate shape.The outer cover 16 has planer dimensions slightly greater than those ofthe inner cover 14. The circumferential portion of the outer cover 16 iswelded to the fixation rib 12 c of the base 12 over the entirecircumference, and thus airtightly fixed to the base 12.

Note that the housing 10 is formed to have a height (thickness) H of26.1 mm at the maximum or less (see FIG. 4 ) according to the 3.5-inchHDD standard.

In the housing 10, a plurality of, for example, ten magnetic disk 18 asdiscoidal recording media and a spindle motor 19 as a drive motor, whichrotate the magnetic disks 18 are provided. The spindle motor 19 isdisposed on the bottom wall 12 a. Each of the magnetic disks 18 isformed into, for example, a disk having a diameter of 96 mm (3.5 inches)and a thickness of 0.5 to 0.635 mm, and comprises a substrate formed of,for example, a nonmagnetic material such as glass or aluminum andmagnetic recording layers respectively formed on an upper surface (afirst surface) and a lower surface (a second surface) of the substrate.In the embodiment, an aluminum substrate is employed. The magnetic disks18 each are fit with a hub, which will be described later, of thespindle motor 19 so as to be coaxial with each other and further clampedby a clamp spring 20. Thus, the magnetic disk 18 is supported to belocated parallel to the bottom wall 12 a of the base 12. The magneticdisks 18 are rotated at a predetermined number of revolutions by thespindle motor 19. Note that the number of magnetic disks 18 loaded maynot necessarily be 10, but may be eleven or more.

In the housing 10 are provided a plurality of magnetic heads 17 whichrecord and reproduce data with respect to the respective magnetic disks18, and an actuator assembly 22 supporting the magnetic heads 17 to bemovable relative to the respective magnetic disks 18. Further, in thehousing 10 are provided a voice coil motor (VCM) 24 which pivots andpositions the actuator assembly 22, a ramp load mechanism 25 whichmaintains, when a magnetic head 17 moves to an outermost circumferenceof the respective magnetic disk 18, the magnetic head 17 at an unloadposition spaced from the magnetic disk 18, and a flexible printedcircuit unit (FPC unit) 21 on which electronic components such asconversion connectors and the like are mounted.

The actuator assembly 22 comprises an actuator block 29 with a throughhole, a bearing unit (unit bearing) 28 provided in the through hole, aplurality of, for example, eleven arms 32 extending from the actuatorblock 29, a suspension assembly (a head gimbal assembly, which may bereferred to as HGA) 30 attached to each arm 32 and the magnetic head 17supported on the suspension assembly 30. With the bearing unit 28, theactuator block 29 is supported rotatably around the support shaft 26provided to stand on the bottom wall 12 a.

The FPC unit 21 incudes substantially rectangular-shaped base portion 21a bent into an L shape, a slim strip shaped relay portion 21 b extendingfrom one side edge of the base portion 21 a and a joint portion providedto continuous to a distal end of the relay portion 21 b, which are allintegrated into one body. The base portion 21 a, the relay portion 21 band the joint portion 21 c constitute the flexible printed circuit board(FPC).

On the base portion 21 a, electronic components such as conversionconnectors, which will be described later, a plurality of capacitors andthe like are mounted and are electrically connected to the wiring of theFPC. On the base portion 21 a, a metal plate functioning as areinforcement plate is attached. The base portion 21 a is disposed onthe bottom wall 12 a of the base 12. The relay portion 21 b extends froma side edge of the base portion 21 a towards the actuator block 29 ofthe actuator assembly 22. The joint portion 21 c, provided in anextending end of the relay portion 21 b, is attached to a side surface(installation surface) of the actuator block 29 and fixed with screws. Alarge number of connection pads are provided in the joint portion 21 c.Each of the magnetic heads 17 of the actuator assembly 22 iselectrically connected to a respective connection pad of the jointportion 21 c via a wiring member.

FIG. 2 is a plan view showing the HDD from a rear surface side and FIG.3 is an enlarged plan view of a motor joint portion in FIG. 2 .

As seen in FIG. 2 , a printed circuit board 40 is disposed on an outersurface of the bottom wall 12 a of the base 12, and fixed to the bottomwall 12 a with a plurality of screws S1 and S2. In this embodiment, theprinted circuit board 40 is formed into a size of about ¼ to ⅓ of thearea of the bottom wall 12 a and is located in a location which does notoverlap a region opposing the magnetic disks 18 and a region opposing anarea where the actuator assembly 22 is movable, that is, a location inthe outer surface of the bottom wall 12 a, which is off from theseregions. In the embodiment, the printed circuit board 40 is provided ina region opposing one end of the bottom wall 12 a, where the VCM 24 andFPC unit 21 are provided. Further, in the embodiment, a recess with ashape corresponding to the printed circuit board 40 is formed in theouter surface of the bottom wall 12 a. This recess has a depthcorresponding to the thickness of the printed circuit board 40 includingthe mounted electronic components, and the printed circuit board 40 isdisposed in the recess to be overlaid thereon.

On the printed circuit board 40, a relay connector 42 connected to aconnector of the FPC unit 21, an interface connector 44 to be connectedto an external equipment, a motor drive IC 71 and others electroniccomponents (not shown) are mounted. The printed circuit board 40 isconfigured as a controlling unit to control operation of the spindlemotor 19 and control operation of the VCM 24 and the magnetic heads 17via the FPC unit 21.

As seen in FIG. 2 , the printed circuit board 40 is formed into such ashape that avoids the region opposing the magnetic disks and theactuator movable region, which is a shape with a constricted portionhaving a width Xl. In the constriction portion, the wiring for I/Fsignals, DRAM signals, VCM signals and various power sources need to bepassed. Therefore, in the embodiment, the printed circuit board 40 isconfigured as, for example, a six-layered printed circuit board, inwhich the wiring for the I/F signals is formed on a surface layer of theboard, the wiring for the DRAM signal and the wiring for the powersources are formed in an inner layer of the board and the wiring for theVCM is formed on a rear layer of the board, thus realizing theabove-described wiring.

Further, in the printed circuit board 40, the portion of the board,which is close to the location where the motor drive IC 71 is mounted,is formed into a relatively slim shape, and with this structure, thereis a possibility that the circuit board greatly warps due to therepulsion force by the IC heat radiation sheet. Therefore, in theembodiment, the printed circuit board 40 is formed to have a thicknessof, for example, 0.8 mm, so as to increase the rigidity of the board.Further, the screw S1 is added to a location near the motor drive IC 71,thereby preventing the warping of the board.

At a plurality of points on the outer surface of the bottom wall 12 a,for example, two locations of side edge portions on each long side edge,bosses 52 of a predetermined height are provided to project. A screwhole 53 for fixing the HDD is formed in each of the bosses 52.

The four bosses 52 are processed plainly so that upper surfaces thereof(user tap surfaces) are located in the same plane.

The HDD is installed so that the upper surfaces of the four bosses 52are brought into contact with the installation surface. That is, theupper surfaces of the bosses 52 are a lowermost surface ML of the base12.

As shown in FIGS. 2 and 3 , a shaft 46 of the spindle motor 19 isprovided to stand on the bottom wall 12 a. A proximal end of the shaft46 is fit with the through hole formed to penetrate the bottom wall 12a. In an outer surface of the bottom wall 12 a, a recess 50 of apredetermined shape, which will be described later, is formed around theshaft 46. The recess 50 is recessed by a predetermined depth from theouter surface, and thus a step portion 54 is formed in a border betweenthe outer surface of the bottom wall 12 a and the recess 50.

A strip-shaped flexible printed circuit board (FPC) 60 is attached andfixed as a wiring member on the outer surface of the bottom wall 12 a.The FPC 60 includes a base insulating layer of polyimide or the like, aconducting layer formed on the base insulating layer, which constitutesa plurality of wires, contact pads and the like, and a protective layerwhich covers the conducting layer. The FPC 60 extends from the printedcircuit board 40 to the vicinity of the shaft 46 in a diametricaldirection of the magnetic disk 18. The FPC 60 includes a first endportion 60 a located between the printed circuit board 40 and the outersurface of the bottom wall 12 a, a second end portion 60 b disposed inthe recess 50, a plurality of, for example, four first contact pads 62 aprovided in the first end portion 60 a and a plurality of, for example,four second contact pads 62 b provided in the second end portion 60 b.The first contact pads 62 a and the second contact pads 62 b areelectrically connected to each other via the wiring of the FPC 60.

The first end portion 60 a and the first contact pads 62 a are placed inpositions further outer side from an outer circumference of therespective magnetic disk 18. The first contact pads 62 a is joined tothe printed circuit board 40 by soldering to be electrically connectedto the printed circuit board 40. As will be discussed later, to thesecond contact pads 62 b, a lead wire W drawn out from a coil of thespindle motor 19 is joined by soldering. Further, an adhesive AD isfilled into the recess 50 so as to cover the second end portion 60 b andthe solder joint.

FIG. 4 is a cross section of the HDD taken along line A-A of FIG. 2 . InFIG. 4 , a straight line ML indicates the lowermost surface of the base12. As described above, the maximum height H of the housing 10, that is,the height H between the lowermost surface ML and the upper surface ofthe outer cover (the top cover) 16 is set to the maximum height of 26.1mm or less according to the 3.5-inch HDD standard.

As shown, the spindle motor 19 includes, for example, the shaft 46provided to stand substantially perpendicular on the bottom wall 12 a, asubstantially cylindrical spindle hub 64 rotatably supported around theshaft 46, a stator coil CS fixed to the bottom wall 12 a and disposedaround the shaft 46 and a cylindrical magnet M attached to an innerperipheral surface of the spindle hub 64 and opposing the stator coilCS.

The proximal end of the shaft 46 is inserted to and fit with the throughhole 67 formed in the bottom wall 12 a.

The spindle hub 64 includes an outer circumferential surface locatedcoaxial with the shaft 46 and an annular flange 65 formed to beintegrated with a lower end (on a bottom wall 12 a side) of the outercircumferential surface. The flange 65 includes an annular disk mountingsurface 72 on which a respective magnetic disk 18 is placed. The lowerend of the spindle hub 64 and the flange 65 opposes the inner surface ofthe bottom wall 12 a with a gap of, for example, about 0.4 mmtherebetween.

The magnetic disks 18 are engaged with the outer circumferential surfaceof the spindle hub 64 while the spindle hub 64 penetrates through theinner holes thereof. Further, annular spacer rings 66 are mounted on theouter circumferential surface of the spindle hub 64 so that each isinterposed between each adjacent pair of magnetic disks 18. The magneticdisks 18 and the spacer rings 66 are disposed to the on the flange 65 ofthe spindle hub 64 in order while alternately attached to the spindlehub 64 to be stacked one on another. Inner circumferential portions ofthe magnetic disks 18 and the spacer ring 66 are pushed to a flange 65side by a clamp spring 20 attached to an upper end of the spindle hub64. Thus, the ten magnetic disks 18 are fixed to the spindle hub 64 withregular intervals between each other in a stacked layer state, and theyare supported integrally with the spindle hub 64 as one body so as to berotatable. The ten magnetic disks 18 are supported at regular intervals,parallel to each other and further substantially parallel to the bottomwall 12 a.

As shown in FIGS. 3 and 4 , in the outer surface of the bottom wall 12a, an arc-shaped recess 50 is formed in a region around the shaft 46. Inthis embodiment, the recess 50 is provided in a region opposing thestator coil CS. The step (slope) 54 is provided in the border betweenthe recess 50 and the outer surface of the bottom wall 12 a. In thisembodiment, when a radius from a central axis of the shaft 46 to aninner circumferential-side edge of the flange 65 is represented by R2(for example, 12.07 mm), the step 54 is provided in a radial position ofradius R1 which is less than the radius R2. That is, the step 54 and therecess 50 are provided in a radial region smaller than the innercircumferential-side edge of the flange 65, that is, a range between theinner circumferential-side edge of the flange 65 and the shaft 46.

The height of the step 54 (=the depth of the recess 50) is set to, forexample, 0.6 mm. In this embodiment, the step 54 is formed as a slopeinclined by approximately 45 degrees to a direction perpendicular to theouter surface of the bottom wall 12 a.

A plurality of, for example, four through holes 70 are formed atlocations opposing the stator coil CS of the bottom wall 12 a. The fourthrough holes 70 each penetrate the bottom wall 12 a and are opened in abottom surface of the recess 50. The lead wires W drawn out from thestator coil CS is drawn out to the recess 50 via the through holes 70.

A second end portion 60 b of the FPC 60 attached to the outer surface ofthe bottom wall 12 a extends into the recess 50 via the step (slope) 54and is attached to the step 54 and the bottom surface of the recess 50.The lead wires W are joined by soldering to four second connection pads62 b of the second end portion 60 b with a solder S, respectively. Thus,the stator coil CS is electrically connected to the printed circuitboard 40 via the FPC 60.

Further, the adhesive AD is filled into the recess 50 and the throughholes 70. The adhesive AD covers the second end portion 60 b, the solderjoint and the lead wires W and airtightly seals each of the throughholes 70. Here, the step 54 prevents spreading of the adhesive AD to theoutside and thus the adhesive AD is filled and placed only in the recess50. The adhesive AD is provided in the recess 50, and therefore abulging portion of the adhesive AD is contained lower than the lowermostsurface without overflowing the lowermost surface ML of the base 12.

Thus, it is no longer necessary to consider the bulging portion of theadhesive AD in a region opposing the flange 65, and therefore itsuffices if the height of the outer surface of the bottom wall 12 a,particularly, the attaching surface of the FPC 60, that is, the intervalbetween the attaching surface and the lowermost surface ML is decided inconsideration of the space merely for the thickness of the FPC 60, andit can be set to about 0.5 mm. Further, in the region, the interval isreduced, that is, by a depth of the recess 50 of 0.6 mm, the outersurface of the bottom wall 12 a can be lowered.

According to the HDD of the first embodiment configured as above, thesecond end portion 60 b of the FPC 60 is disposed in the recess 50formed in the outer surface of the bottom wall 12 a and further theadhesive AD for the overcoat is filled in the recess 50. With thisconfiguration, the bulging portion of the adhesive AD never exceeds thelowermost surface ML of the base 12, thus making it possible to preventwobbling of the HDD when placed horizontally or the height of the devicefrom exceeding the value of the specification. Further, by the depth ofthe recess 50, the outer surface of the bottom wall 12 a can be loweredand the height position of the disk attaching surface 72 of the flange65 can be lowered. Thus, the number of magnetic disks to be loaded andthe interval between magnetic disks can be increased, and thus an HDD inwhich ten or more magnetic disks are loadable can be obtained.

The thickness T1 of the bottom wall 12 a of the region (opposing region)opposing the flange 65 can be maintained as the same thickness asconventional techniques, and therefore the castability of the base 12 isnot adversely affected. Thus, it is possible to cast a high-quality base12 in which extremely few casting cavities, which can give rise to leakpaths and can endure the sealing of helium for a long time.

Further, in the embodiment, the step 54 is formed into an inclinedslope, and thus both effects of smooth attachment of the FPC 60 and theprevention of excessive spreading of the adhesive AD can be obtained atthe same time.

Next, an HDD according to another embodiment will be described. In thisembodiment provided below, portions equivalent to those of the firstembodiment are denoted by the same reference numbers and detailedexplanations thereof will be omitted or simplified, and suchexplanations will be mainly provided for portions different from thoseof the first embodiment.

Second Embodiment

FIG. 5 is a cross section of an HDD according to the second embodiment.

In the second embodiment, as shown in FIG. 5 , the height of the outersurface of the bottom wall 12 a is set similar to that of the firstembodiment and the thickness T1 of the bottom wall 12 a is set unchangedto 1.1 mm, which is similar to that of the conventional techniques whencasting. Further, in the inner surface of the bottom wall 12 a, theregion opposing the flange 65 is cut by 0.3 mm, and thus the thicknessT1 of the bottom wall 12 a is set to about 0.8 mm. In place, theinstallation position of the flange 65 is lowered to the bottom wall 12a side so as to decrease the height of the disk mounting surface 72 ofthe flange 65 by 0.9 mm. Here, the height (interval) from the lowermostsurface ML of the base 12 to the disk mounting surface 72 is 3.7 mm orless, for example, 3.655 mm.

In the second embodiment as well, the printed circuit board 40 is formedand disposed in a similar manner as that of the first embodiment. Thatis, the printed circuit board 40 is formed to have a size of about ¼ to⅓ of the area of the bottom wall 12 a and is provided in a region whichdoes not overlap the region opposing the respective magnetic disk 18 andthe region opposing the movable region of the actuator assembly 22, thatis, the region of the outer surface of the bottom wall 12 a, which isoff of these regions. Further, in the embodiment, the printed circuitboard 40 is disposed to be overlaid on the recess formed in the outersurface of the bottom wall 12 a.

In the HDD of the above-described configuration, the thickness of thebottom wall 12 a when casting the base 12 is same as that of theconventional technique, that is, 1.1 mm, and therefore castabilityequivalent to that of the conventional technique is maintained. Whenassuming the thickness of the flange 65 and the interval between theflange 65 and the bottom wall 12 a are equivalent to those of theconventional HDD, the height position of the disk attaching surface 72of the flange 65 can be lowered by 0.9 mm. Therefore, for the portion of0.9 mm, the number of magnetic disks to be loaded can be increased. Forexample, let us suppose the case where ten 0.5 mm-thick magnetic disksand nine 1.58 mm-thick spacer rings are disposed in a multi-layeredmanner on the disk attaching surface 72 of the flange 65. In this case,a total thickness of the multiplayer is: 0.5×10+1.58×9=19.22 mm. Thus,ten magnetic disks can be loaded without substantially changing theheight of the uppermost surface of the magnetic disk.

Note that the first end portion 60 a and the first contact pads 62 a ofthe FPC 60 connected to the printed circuit board 40 are disposed on anouter region of the radius R of the magnetic disk 18. Therefore, inorder to lower the disk mounting surface 72 of the flange 65 by 0.9 mm,it is not necessary to form an extremely thin portion in a region of thebottom wall 12 a directly under the magnetic disk 18, and thus thecastability of the base 12 can be maintained.

In the embodiment, the height from the lowermost surface of the base tothe lowermost surface of the disk is lowered by 0.9 mm as compared tothe conventional magnetic disc devices, and therefore it is difficult todispose the printed circuit board 40 in a region opposing the magneticdisk. Thus, in this embodiment, as described above, the printed circuitboard 40 is placed in a region which does not overlap the regionopposing the magnetic disk 18 and the range opposing the movable regionof the actuator assembly 22. Thus, ten or more magnetic disks 18 can beloaded on the housing 10 while maintain such a thickness of the base asto satisfy the castability necessary to seal He even in the regiondirectly under the magnetic disk.

In addition, in the second embodiment as well, advantageous operationaleffects similar to those of the above-described first embodiment can beobtained.

First Modified Example

With reference to FIG. 5 , the first modified example of the secondembodiment will be described. According to the first modified example,the mechanical processing amount of the region of the bottom wall 12 aopposing the flange 65 is increased by 0.1 mm, and the thickness of thebottom wall 12 a after the processing is 0.7 mm. The internal betweenthe flange 65 and the bottom wall 12 a is reduced to 0.4 to 0.25 mm.Further, the thickness of the flange 65 is reduced to 1.92 to 1.72 mm.Thus, the height position of the disk mounting surface 72 of the flange65 can be lowered by 1.35 mm. The height (interval) from the lowermostsurface ML of the base 12 to the disk mounting surface 72 is 3.7 mm orlower, for example, 3.17 mm.

In the first modified example, for example, let us suppose the casewhere ten 0.635 mm-thick magnetic disks and nine 1.488 mm-thick spacerrings are disposed in a multi-layered manner on the disk attachingsurface 72 of the flange 65. In this case, a total thickness of themultiplayer is: 0.635×10+1.484×9=19.706 mm. Thus, ten magnetic disks 18can be loaded without substantially changing the height of the uppermostsurface of the magnetic disk.

While certain embodiments or modifications have been described, theseembodiments or modifications have been presented by way of example only,and are not intended to limit the scope of the inventions. Indeed, thenovel embodiments and modifications described herein may be embodied ina variety of other forms; furthermore, various omissions, substitutionsand changes in the form of the embodiments and modifications describedherein may be made without departing from the spirit of the inventions.The accompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of theinventions.

In the embodiments and the modified example, described above, the numberof magnetic disks to be loaded is not limited to ten, but may be elevenor more. The thickness of the magnetic disk is not limited to 0.635 mmor 0.5 mm, but may be variously changed as needed. Similarly, thediameter of the magnetic disks is not limited to 96 mm, but may be, forexample, 95 mm or 97 mm. The number of through holes which pass the leadwires of the stator coil is not limited to four but may be three orless. The abutting surface of the boss portion 52 is not limited to aprocessing surface, but may be partially or entirely casting surface.The adhesive is not limited to one type, but two or more types ofadhesives may be compositely used. For example, such a structure may beadopted that a highly sealing adhesive is filled in the through holes 70and some other type of adhesive is applied to the recess 50.

What is claimed is:
 1. A disk device comprising: a housing comprising abase including a bottom wall and a cover fixed to the base and opposingthe bottom wall with an interval therebetween and having a heightdefined by a standard of 3.5-inch disk devices; ten or more magneticdisks rotatably disposed in the housing; a head actuator comprising aplurality of magnetic heads configured to process data with respect tothe magnetic disks, respectively, and rotatably provided in the housing;a flexible printed circuit unit disposed on the bottom wall in thehousing and mounted with electric components including a connector, theflexible printed circuit unit being connected to the head actuator; anda printed circuit board mounted with electronic components including aninterface connector, a relay connector, and a motor drive IC, disposedat a location off from a region opposing the magnetic disks to oppose anouter surface of the bottom wall and formed into a size of ⅓ or less ofan area of the bottom wall, the relay connector being connected to theconnector of the flexible printed circuit unit.
 2. The disk device ofclaim 1, wherein ten magnetic disks of a thickness of 0.635 mm and adiameter of 3.5 inches are stacked on and supported by a hub of a motorprovided in the housing.
 3. The disk device of claim 1, wherein alow-density gas having a density lower than that of air is enclosed inthe housing.
 4. The disk device of claim 1, wherein the printed circuitboard includes a constricted portion, and the motor drive IC is providedat a location apart from the constricted portion.
 5. The disk device ofclaim 1, wherein the printed circuit board is a multi-layered printedcircuit board having six layers.
 6. The disk device of claim 1, whereinthe printed circuit board has a thickness of 0.8 mm.
 7. The disk deviceof claim 1, wherein the housing includes a recess formed in the outersurface of the bottom wall and having a shape corresponding to a shapeof the printed circuit board, and the printed circuit board is disposedin the recess to be overlaid on the recess.
 8. The disk device of claim7, wherein the recess has a depth corresponding to a thickness of theprinted circuit board including the mounted electronic components.
 9. Adisk device comprising: a housing comprising a base including a bottomwall, an inner cover fixed to the base to close an upper opening of thebase and opposing the bottom wall with an interval therebetween, and anouter cover overlaid on the inner cover and welded to the base, thehousing having a height defined by a standard of 3.5-inch disk devicesand a low-density gas having a density lower than that of air beingenclosed in the housing; ten or more magnetic disks rotatably disposedin the housing; a head actuator comprising a plurality of magnetic headsconfigured to process data with respect to the magnetic disks,respectively, and rotatably provided in the housing; a flexible printedcircuit unit disposed on the bottom wall in the housing and mounted withelectric components including a connector, the flexible printed circuitunit being connected to the head actuator; and a printed circuit boardmounted with electronic components including an interface connector, arelay connector, and a motor drive IC, disposed at a location off from aregion opposing the magnetic disks to oppose an outer surface of thebottom wall and formed into a size of ⅓ or less of an area of the bottomwall, the relay connector being connected to the connector of theflexible printed circuit unit.